The invention relates generally to an unresettable switch which will open a circuit when the ambient temperature around the circuit is increased to a predetermined level.
Switches of the type generally described have become necessary to protect various circuitry in devices, such as appliances, etc., from the hazards of high temperatures generated therein. Prior art devices of the type generally described are typically multipiece units relying upon a conductive casing to carry current in the circuit from one lead to the other within the switch. Commercially available switches of this type typically utilize a large number of individual parts, for example between nine to eleven parts are used in known commercial embodiments of this type. Thus, in addition to the use of a conductive case, which will not permit x-ray quality control examination and which, conceivably, could contribute to a shorting situation within the circuitry, the number of parts required significantly contributes to the cost of such a device. Other prior art attempts to obtain a thermal switch device of the type described involve the dipping of the switch extremities of a pair of spring lead wires with a heat-fusible material and thereafter conformally encasing the portion of the leads and totally conformally coating the heat-fusible material with an insulative structure. While this type of device, and the type first described above, do provide a satisfactory component, there appears to be certain inherent production difficulties, such as the difficulty of controlling the volume of the dip, the time for the dip, etc., that must be overcome in order to manufacture the devices in an efficient production basis.